Powder feeder for material deposition systems

ABSTRACT

A method and apparatus for embedding features and controlling material composition in a three-dimensional structure ( 130 ) is disclosed. The invention enables the control of material characteristics, within a structure ( 130 ) made from a plurality of materials, directly from computer renderings of solid models of the components. The method uses stereolithography and solid model computer file formats to control a multi-axis head ( 480 ) in a directed material deposition process ( 123 ). Material feedstock ( 126, 127 ) is deposited onto a pre-heated substrate ( 19 ). Depositions ( 15 ) in a layer-by-layer pattern, defined by solid models ( 141, 146 ), create a three-dimensional article having complex geometric details. Thermal management of finished solid articles ( 250 - 302 ), not available through conventional processing techniques, is enabled by embedded voids ( 152 ) and/or composite materials ( 126, 127 ), which include dissimilar metals ( 210, 216 ). Finished articles control pressure drop and produce uniform coolant flow and pressure characteristics. High-efficiency heat transfer is engineered within a solid structure by incorporating other solid materials with diverse indexes. Embedding multi-material structures ( 132, 134 ) within a normally solid component ( 141 ) produces articles with diverse mechanical properties. Laser and powder delivery systems ( 420, 170 ) are integrated in a multi-axis deposition head ( 480 ) having a focused particle beam ( 502 ) to reduce material waste.

CROSS-REFERENCES TO RELATED PATENT APPLICATIONS & CLAIMS FOR PRIORITY

This application is a continuation application of U.S. patentapplication Ser. No. 10/128,658, entitled “Forming Structures from CADSolid Models”, filed on Apr. 22, 2002, which is a continuation-in-partapplication of U.S. patent application Ser. No. 09/568,207, now U.S.Pat. No. 6,391,251, entitled Forming Structures from CAD Solid Models,filed on May 9, 2000, which claims the benefit of the filing of U.S.Provisional Patent Application Ser. No. 60/143,142, entitled“Manufacturable Geometries for Thermal Management of ComplexThree-Dimensional Shapes”, filed on Jul. 7, 1999. The specifications andclaims of all of the above references are hereby incorporated herein byreference.

FIELD OF THE INVENTION

The present invention relates to the field of direct material depositionprocesses which allow complex structures to be fabricated efficiently insmall lots to meet stringent requirements of a rapidly changingmanufacturing environment. More particularly, the invention pertains tothe fabrication of three-dimensional metal parts directly from acomputer-aided design (CAD) electronic “solid” model. The invention alsoprovides methods which use existing industry-standard computer fileformats to create unique material structures including those havingthermal characteristics embedded within them. The invention addressesmethods to control direct material deposition processes to achieve anet-shaped or near net-shaped article, and to fabricate metal articleshaving exceptional material properties and dimensional repeatability.

BACKGROUND OF THE INVENTION

Manufacturing techniques or technologies generally known as “layeredmanufacturing” have emerged over the last decade. For metals, the usualshaping process forms a part by removing metal from a solid bar or ingotuntil the final shape is achieved. With the new technique, parts aremade by building them up on a layer-by-layer basis. This is essentiallythe reverse of conventional machining. According to the paper appearingat the Internet site of Helsinki University of Technology, the firstcommercial process was presented in 1987. The process then was veryinaccurate, and the choice of materials was limited. The parts wereconsidered, therefore, prototypes and the process was called rapidprototyping technology (RPT). The prior art has advanced, however, to apoint where it has been favorably compared too conventionallynumerically controlled (NC) milling techniques. Considerable savings intime, and therefore cost, have been achieved over conventional machiningmethods. Moreover, there is a potential for making very complex parts ofeither solid, hollow or latticed construction.

Stereolithography technique (SLT), sometimes known as solid freeformfabrication (SFF), is one example of several techniques used tofabricate three-dimensional objects. This process is described in theHelsinki University of Technology paper. A support platform, capable ofmoving up and down is located at a distance below the surface of aliquid photo polymer. The distance is equal to the thickness of a firstlayer of a part to be fabricated. A laser is focused on the surface ofthe liquid and scanned over the surface following the contours of aslice taken through a model of the part. When exposed to the laser beam,the photo polymer solidifies or is cured. The platform is moveddownwards the distance of another slice thickness and a subsequent layeris produced analogously. The steps are repeated until the layers, whichbind to each other, form the desired object. A He—Cd laser may be usedto cure the liquid polymer. The paper also describes a process of“selective laser sintering.” Instead of a liquid polymer, powders ofdifferent materials are spread over a platform by a roller. A lasersinters selected areas causing the particles to melt and solidify. Insintering, there are two phase transitions, unlike the liquid polymertechnique in which the material undergoes but one phase transition: fromsolid to liquid and again to solid. Materials used in this processincluded plastics, wax metals and coated ceramics. A number of Patentsand other disclosures have preceded and followed these processes,including the following:

U.S. Pat. No. 4,323,756, issued on Apr. 6, 1982 to Clyde O. Brown, etal., entitled Method for Fabricating Articles by Sequential LayerDeposition, discloses a method for the production of bulk rapidlysolidified metallic objects of near-net shape, by depositing multiplethin layers of feedstock using an energy beam to fuse each layer onto asubstrate. The feedstock may be in the form of metal powder or wire. Anet shaped or near-net shaped article is one which approximates all ofthe desired features of its contemplated design so that little or nofinishing work is required.

In his U.S. Pat. No. 4,724,299, dated Feb. 9, 1988, Albert W. Hammekedescribes a laser spray nozzle in which a beam passageway between theend portions permits a laser beam to pass through. A housing surrounds asecond end portion and forms an annular passage, coaxial with the beampassageway. A cladding powder supply system is connected with theannular passage so that the powder exits the coaxial opening with thebeam. The laser beam melts the powder which is deposited on a targetsubstrate. The powder distribution system is contained within the nozzleassembly.

A laser spray nozzle assembly is a part of the Axial Flow Laser PlasmaSpraying apparatus disclosed by Eric J. Whitney et al. in their August1991 U.S. Pat. No. 5,043,548. The apparatus for depositing a feedmaterial onto a substrate, has a plasma confinement chamber into which alaser beam is focused, the focal point being at a distance sufficientlyfar from the substrate that the substrate, is not melted. Finely dividedfeed material in a carrier gas flow is fed axially into the confinementchamber along the direction of the laser beam and melted into the plasmaformed in the interaction of the laser beam, the feed material and thegas at the focal point. The feed material is then directed to depositonto the substrate while the plasma energy is largely confined withinthe apparatus by the confinement chamber and constriction of the flowpath upstream of the chamber.

A Rapid Prototyping System is disclosed by Joshua E. Rabinovich in U.S.Pat. No. 5,578,227, issued Nov. 26, 1996. The system involves a modelmaking method and apparatus which projects a laser beam, circularpolarizes the beam and directs the circular polarized beam for fusing arectangular wire to a substrate or a previously fused wire on a targetstage. The disclosure is differentiated by fusing the depositedfeedstock to bond to a previously deposited layer without substantiallyaltering the cross-section of the newly deposited material.

Such a deposition process would seem to have substantial problems ofwarping and distorting the deposited layers because of incompletemelting of feedstock material. Unlike Rabinovich's disclosed process, apowder deposition completely consumes the feedstock material in thethree-dimensional net shape. The powder's cross-section and materialproperties are significantly altered. Rabinovitch does not disclose howthe properties of the deposited material are controlled in hisinvention.

U.S. Pat. No. 5,697,046, dated Dec. 9, 1997 and entitled CompositeCermet Articles and Method of Making was issued to Edward V. Conley. Itdiscloses methods for making and using and articles comprisingferromagnetic cermets, preferably carbides and more preferably tungstencarbide having at least two regions exhibiting at least one propertythat differs. The cermets are manufactured by juxtaposing and densifyingat least two powder blends having different properties. The methodsdescribed are very specific to cermets and do not employ solid modelsand automated processes.

U.S. Pat. No. 5,705,117 dated Jan. 6, 1998 discloses a Method ofCombining Metal and Ceramic Inserts Into Stereolithography Components.Kurt Francis O'Connor et al. describe a stereolithography process fordeveloping a prototype part in which inserts of non-photo polymermaterial are included in the resulting part so as to develop afunctioning prototype part. In order to allow the inserts to be placedwithin the developing prototype part, a series of STL files are definedfor forming the part in individual sections. The method is very specificto metal-ceramic composite structures for PC boards. It is not a directfabrication method for three-dimensional objects with graded or multiplematerial structures.

Direct fabrication of three-dimensional metal parts by irradiating athin layer of metal powder mixture is described in U.S. Pat. No.5,393,613, entitled Composition for Three-Dimensional Metal fabricationUsing a Laser, and issued Feb. 28, 1995. Colin A. MacKay uses atemperature equalization and unification vehicle in the mixture which ismelted by a laser, selectively applied to form a solid metal film. Thevehicle protects the molten metal from oxidation. The metal powder cancontain an elemental metal or several metals. The material has a lowermelting temperature because of the vehicle, which is essentially a flux.The method does not create structures of gradient material.

U.S. Pat. No. 5,707,715, issued to L. Pierre deRochemont et al. on Jan.13, 1998, presents a disclosure of metal-ceramic composite comprising ametal member bonded to a ceramic oxide member through a covalent bondformed at temperatures less than 880 degrees Centigrade. Metal-ceramiccomposites are also described that are so constructed to controlinternal stress or increase crack resistance within the ceramic memberunder applied thermal or mechanical loads. The disclosure does notreveal a direct fabrication method for three-dimensional objects withgraded or multiple material structures.

U.S. Pat. No. 5,126,102, entitled Fabricating Method of CompositeMaterial, was granted to Masashi Takahashi on Jun. 30, 1992, anddescribes a method of preparing a composite material, excellent in jointstrength and heat conductivity. More specifically, it describes a methodof preparing a composite material composed of high melting temperaturetungsten (W) material and low melting temperature copper (Cu) materialby forming pores in the tungsten to obtain a substrate with distributedporosity. The method forms a high-porosity surface in at least oneregion of the substrate, the porosity gradually decreasing outward fromthe region. A second step impregnates the tungsten material with thecopper material in the porous surface forming a gradient material oftungsten and copper. The patent describes the advantages of gradientmaterials, however, it does not discuss the use of solid models toachieve the shape of the gradient article. Direct material depositionprocesses produce three-dimensional parts by sequential layer depositionof feedstock material in powder or wire form.

Robert A. Sterett et al., in their aptly named U.S. Pat. No. 5,746,844,issued on May 5, 1998, disclose a Method and Apparatus for Creating aFree-Form Three-Dimensional Article Using A Layer-By-Layer Deposition ofmolten Metal and Using Stress-Reducing Annealing Process On theDeposited Metal. A supply of substantially uniform droplets of desiredmaterial having a positive or negative charge, is focused into a narrowstream through an alignment means which repels each droplet toward anaxis through the alignment means. The droplets are deposited in apredetermined pattern at a predetermined rate onto a target to form thethree-dimensional article without use of a mold of the shape of thearticle. The disclosure reveals means for reducing stress by annealingportions of the deposited droplets which newly form a surface of the 3-Darticle. Melting of the metal is not done by laser and molten metal.Metal powder is carried from a liquid supply to the target surface. Theinvention produces “fully dense” article of one metal or an alloymaterial having uniform density, no voids and no porosity. The methodallows creation of part overhangs without using supports, by relying onthe surface tension properties of the deposition metal.

U.S. Pat. No. 5,837,960 to Gary K. Lewis, of Los Alamos NationalLaboratory, et al. was filed on Nov. 30, 1995 and issued on Nov. 17,1998. Its title is Laser Production of Articles from Powders. A methodand apparatus are disclosed for forming articles from materials inparticulate form in which the materials are melted by a laser beam anddeposited at points along a tool path to form an article of desiredshape and dimensions. Preferably, the tool path and other parameters ofthe deposition process are established using computer-aided design (CAD)and computer-aided manufacturing (CAM) techniques. A controllerconsisting of a digital computer directs movement of a deposition zonealong the tool path and provides control signals to adjust the apparatusfunctions, such as the speed at which a deposition head which deliversthe laser beam and powder to the deposition zone moves along the toolpath. The article is designed using a commercially available CAD programto create a design file. A “cutter location file” (CL) is created fromthe design file and an adapted, commercially available CAM program.User-defined functions are established for creating object features inthe adapted CAM program. The functions are created by passing an“electronic plane” through the object feature. A planar figure createdin the first plane at the intersection with the feature is a firstportion of the tool path. A second plane is passed through the featureparallel to the first plane. The second plane defines a second toolpath. The end of the tool path in the first plane is joined to thebeginning of the tool path in the second plane by a movement command.The process is continued until the tool path required to make thefeature is complete.

Lewis et al. describe certain methods of preheating an article support(substrate) to overcome the fact that without it, an article supportwill be cold when the deposition is started in comparison to thematerial on which deposition is later done in the fabrication process.Computer modeling of heat flow into, through and out of an article andthe data generated from such modeling imported into the CAM program issuggested. The fabrication of articles of two different materials isaddressed by forming a joint between dissimilar metals by changingpowder compositions as the joint is fabricated. As an example, one couldintroduce a third material as an interlayer between mild steel and 304stainless steel. The interlayer material might be a Ni—Cr—Mo alloy suchas Hastelloy S.

U.S. Pat. No. 5,993,554 to David M. Keicher et al., dated Nov. 30, 1999and entitled Multiple Beams and Nozzles to Increase Deposition Rate,describes an apparatus and method to exploit desirable material andprocess characteristics provided by a lower power laser materialdeposition system. The invention overcomes the lower material depositionrate imposed by the same process. An application of the invention isdirect fabrication of functional, solid objects from a CAD solid model.A software interpreter electronically slices the CAD model into thinhorizontal layers that are subsequently used to drive the depositionapparatus. A single laser beam outlines the features of the solid objectand a series of equally spaced laser beams quickly fill the featurelessregions. Using a lower power laser provides the ability to create a partthat is very accurate, with material properties that meet or exceed thatof a conventionally processed and annealed specimen of similarcomposition. At the same time, using multiple laser beams to fill infeatureless areas allows the fabrication process time to besignificantly reduced.

In an article entitled The Direct Metal-Deposition of H13 Tool Steel for3-D Components by J. Mazurnder et al., the authors state that the rapidprototyping process has reached the stage of rapid manufacturing viadirect metal deposition (DMD) technique. Further, the DMD process iscapable of producing three-dimensional components from many of thecommercial alloys of choice. H13 is a material of choice for the tooland die industry. The paper reviews the state of the art of DMD anddescribes the microstructure and mechanical properties of H13 alloydeposited by DMD.

The problem of providing a method and apparatus for optimum control offabrication of articles having a fully dense, complex shape, made fromgradient or compound materials from a CAD solid model, is a majorchallenge to the manufacturing industry. Creating complex objects withdesirable material properties, cheaply, accurately and rapidly has beena continuing problem for designers. Producing such objects inhigh-strength stainless steel and nickel-based super alloys, toolsteels, copper and titanium has been even more difficult and costly.Having the ability to use qualified materials with significantlyincreased strength and ductility will provide manufacturers withexciting opportunities. Solving these problems would constitute a majortechnological advance and would satisfy a long felt need in commercialmanufacturing.

SUMMARY OF THE INVENTION

The present invention pertains generally to a class of materialdeposition processes that use a laser to heat and, subsequently, fusepowder materials into solid layers. Since these layers can be depositedin sequential fashion to ultimately form a solid object, the ability toalter the material properties in a very localized fashion has farreaching implications.

The present invention comprises apparatus and method for fabrication ofmetallic hardware with exceptional material properties and gooddimensional repeatability. The invention provides a method forcontrolling material composition, and thus material characteristics,within a structure made from a plurality of materials, directly fromcomputer renderings of solid models of the desired component. Bothindustry-accepted stereolithography (STL) file format as well as solidmodel file format are usable.

One embodiment of the invention is used to form embedded features in athree-dimensional structure. A plurality of separate material feedstockare fed into a directed material deposition (DMD) process which places aline of molten material onto a substrate. The depositions are repeatedin a layer-by-layer pattern, defined by solid models which describe thestructure, to create an article having complex geometric details. Thebulk properties of the deposition are controlled by adjusting the ratioof laser irradiance to laser velocity along the line of deposition.

In addition to external contours, the solid-model computer filesdescribe regions of each separate material, regions of a composite ofthe materials and regions of voids in each layer or “slice.” Thedepositions are repeated in each of the “slices” of the solid models tocreate the geometric details within the three-dimensional structure.

Heating the substrate and the deposition produces parts with accuratedimensions by eliminating warping of the substrate and deposition. Aprescribed temperature profile is used for processing tempered material.A temperature profile for heat treating may be used to enhance themechanical properties of the part by ensuring the correct materialmicrostructure during processing.

Although the prior use of DMD processes has produced solid structures,the use of this technology to embed features for thermal management ofsolid structures is novel. Embedding voids and/or composite materialregions, enables thermal management engineering techniques for solidstructures that are not available through conventional processingtechniques. In one embodiment of the present invention, a method isprovided to construct a solid structure with integral means to controlits thermal properties.

Active thermal control is provided by forming passages and chambers fora coolant medium. The cross-section area and length of individualembedded structures are made approximately equal to provide uniform flowcharacteristics and pressure in the three-dimensional structure. Passivethermal control is provided by embedding materials having diversethermal indexes.

Another embodiment of the present invention provides methods to locallycontrol the thermal history of a three dimensional structure. Thermalhistory is the temperature variation in the part as a function of time.A part made with high thermal conductivity material in one region and alow thermal conductivity material in another region, will have adifferent thermal variation with time in each region.

In a further embodiment of the present invention, high-efficiency heattransfer is obtained within a three dimensional structure byincorporating regions of other materials within the article. Forexample, in parts having varying cross-sections, heating and cooling inselected regions is controlled to prevent thermal stresses.

In yet another embodiment of the present invention, three dimensionalcomponents are formed in which thermal characteristics such as heatingand cooling rates are engineered into the component.

Embedding multi-material structures within a normally solid componentproduces articles with diverse mechanical properties. Articles havingcomplex internal and external contours such as heat exchangers andturbine blades are easily produced with the methods and apparatusdisclosed.

To enhance the deposition process for manufacture of three-dimensional,multi-material structures with interior cavities either hollow or filledwith diverse material, new apparatus, methods of deposition and materialdelivery are disclosed. These include:

-   -   1. Engineering properties such as tensile strength, toughness,        ductility, etc. into the material layers by reference to a        laser-exposure factor (E) which includes variables of laser        power (p), relative velocity of the deposition (v) and material        constants (a).    -   2. A fast-acting diverter valve for regulating feedstock flow        allows precision depositions of gradient materials. The diverter        valve controls the flow of a stream of a carrier gas and powder        material to the deposition head. The valve comprises one        diverter for a stream of gas only and another for a stream of        gas and powder. The diverters are proportionately controlled so        that the total volumetric flow rate of the powder and gas is        constant, but the mass flow rate of powder to the deposition        head can be quickly varied from no powder to the maximum        available. Waste gas with powder is re-circulated and waste gas        is reclaimed.    -   3. A self-contained, volumetric, low-friction powder feed unit        which allows a user to use extremely low flow rates with a        variety of powder materials; the powder feeder design is a        marked improvement over current disk-style powder feeders in        which the disk typically is buried in powder. In the present        invention, powder flow from a reservoir to a transfer chamber is        limited by the angle of repose of the powder feedstock,        preventing the disk from being overwhelmed and clogged with        powder. The present invention is insensitive to variations in        flow rate of the gas which transports the powder to the        deposition head. The spacing between the feed disk and the        wipers which remove powder from the disk can be greater than in        prior art designs without losing control of powder metering.        This promotes much less wear on the wipers and substantially        improves the life of the powder feed unit.    -   4. A multi-axis deposition head, including the powder delivery        system and optical fiber, laser beam delivery system, moveable        about a plurality of translational and rotational axes; the        relative directions of the powder stream in the deposition        process (123) being coordinated with a control computer (129) in        a plurality of coordinate axes (x, y, z, u, v).    -   5. “Smart” substrates which are useful for construction of        articles with internal spaces, unreachable from the surface, but        serve as a starting point for conventional shaping methods.    -   6. Protection for the fiber optic which delivers a laser beam to        the work piece to prevent catastrophic failure of the fiber        because of beam reflections from the deposition surface, using a        folding mirror, offset from 45 degrees by a small angle, to        image a reflected laser beam at a distance from the fiber optic        face, and water cooling of the fiber optic face.    -   7. A laser beam shutter with a liquid-cooled beam “dump” to aid        testing and adjustment of the fiber optic, laser beam delivery        system.    -   8. Using the surface tension property of melted materials to        creating structures having unsupported overhanging edges.    -   9. Using a rotated plane of deposition or rotating a multi-axis        deposition head to build unsupported overhanging edges.    -   10. Particle beam focusing to reduce material waste.

An appreciation of other aims and objectives of the present inventionmay be achieved by studying the following description of preferred andalternate embodiments, and by referring to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of the prior art, Laser EngineeredNet Shaping (LENS.™.) process showing a vertically-movable laser beam,powder delivery nozzle and a substrate situated upon X-Y positioningstages.

FIG. 2 is a plan view of a sample object used in dimensionalrepeatability of metal deposition experiments.

FIG. 3 is a chart showing deposition layer thickness as a function ofthe volumetric exposure (laser irradiance/velocity) of the metaldeposition measured in several samples.

FIG. 4 depicts a graph of surface finish as a function of powder meshsize and laser power used in creating deposited metal samples.

FIG. 4 a is a graph that demonstrates how material strength of 316stainless steel varies with exposure parameter E.

FIG. 5 is an elevation-view comparison of deformation of three substratesamples exposed to metal depositions using laser beam melting, the mostdeformed substrate having no preheating, the least deformed substratepreheated to 200 degrees centigrade and the intermediate substratepreheated to 100 degrees centigrade.

FIG. 6 schematically depicts in side-view, a metal deposition apparatusaccording to the present invention in which heat is applied to asubstrate by a radiant source, the heating being measured over time by amonitoring source.

FIG. 7 is a side view of the metal deposition apparatus depictingsubstrate heating by a platen having internal heating elements,temperature monitoring being accomplished by sensors in the platen andon the substrate.

FIG. 8 presents a graph of one profile of heating a substrate duringdeposition. Controlling the temperature to a profile insures the correctmaterial microstructure during processing.

FIG. 9 is a side-elevation view comparing two substrates, showingwarping in the upper one which was not heated during depositionprocessing and no warping of the lower one which was heated duringdeposition processing.

FIG. 10 shows yet another profile of thermal heating applied to a partduring fabrication by directed material deposition, the added stepsbeing applied to further improve the properties of the depositedmaterial.

FIG. 11 is a schematic view showing the components of a directedmaterial deposition system for fabricating objects from two differentmetal powders, according to the present invention.

FIG. 12 is a perspective sketch illustrating the concept of capturing asolid model made of one material within a solid model made of adifferent material by means of the present invention.

FIG. 13 is a plan view representing a plane section A-A taken throughthe solid models of FIG. 12, revealing the outer solid model of onematerial, the inner solid model of a second material and the regioncomposed of both materials, graded from the first material to the secondmaterial. Composite cross-hatching illustrates the intersecting solidmodels and the region composed of two or more materials.

FIG. 14 is a plan view of a thin slice of the solid models at sectionA-A wherein a solid model representing a region of a first material iscombined with a solid model representing a region of a second materialto create a central core of one material, an outer region of the firstmaterial and an intermediate region of graded, composite material. Toaid visualization of the process which combines two solid models, thesolid model representing the region containing the first material isexploded from the solid model of the region containing the secondmaterial.

FIG. 14 a is a cutaway view of a fast-acting diverter valve used toregulate powder flow to the work area.

FIG. 14 b is a schematic diagram of the operation of the diverter valveof FIG. 14 a, illustrating how the volumetric flow of powder in a gascarrier is maintained constant.

FIG. 15 is a perspective view of a low-rate powder feed unit.

FIG. 16 is a perspective view of the low-friction, volumetric powderfeed unit seen along view B-B of FIG. 15.

FIG. 16 a is a perspective view of the powder feed disk and wiperassembly, alone, revealing the feed holes, disposed circumferentially inthe disk, which pick up powder from the supply pile.

FIG. 16 b is a graph of average flow rate for 316 stainless steel powderversus feed disk RPM for three test conditions, showing the nearlylinear performance of the powder feeder.

FIG. 16 c shows an elevation view of a directed material deposition,revealing “buttering” layers of a first and second transitionalmaterial, deposited between two dissimilar metals to providemetallurgical compatibility between them.

FIG. 17 is a perspective view of a cross-sectioned mold insert with amold cavity, showing the detail of the conformal cooling passagesintegrated into the mold during manufacture using DMD methods.

FIG. 18 is a perspective view of the whole mold insert showing theinternal geometries as hidden lines, with inlet and outlet ports forcoolant media, fabricated using invention methods disclosed herein.

FIG. 19 is a cross sectional view of a solid, rectangular DMD article,showing the internal cooling passages and an inlet and exit madeintegral with the article.

FIG. 20 is a cross-sectional view of a cylindrical article fabricated bythe deposition method of the present invention, illustrating integralcooling passages.

FIG. 21 is a cross-sectional view of a cylindrical object with complexgeometries of separate cooling passages fabricated into the component,made by DMD.

FIG. 22 is a perspective view of a solid, curved object made by directedmaterial deposition, having the cooling passages following the contourof the outer shape.

FIG. 23 is a perspective view of an airfoil shaped DMD article, such asa turbine blade, with cooling channels fabricated integrally within theairfoil.

FIG. 24 represents a perspective view of a partially constructed “smart”substrate which can be made by DMD methods or by conventional machining.

FIG. 25 is another view of the “smart” substrate in process shown inFIG. 24 to which has been added additional deposited material.

FIG. 26 is a perspective view of the finished “smart substrate” articleshown in process in FIGS. 24 and 25.

FIG. 26 a is a perspective view of a latticed “smart” substrate,depicting tubular cooling channels which support the substrate bearingsurfaces.

FIG. 26 b is a perspective view of a plastic injection mold havingembedded cooling channels of circular cross-section.

FIG. 26 c is view C-C of the plastic injection mold revealed in FIG. 26b.

FIG. 27 reveals a side-view schematic of a method of manufacturingoverhanging structures using 3-axis positioning of the deposition headin respect of the work piece.

FIG. 28 is a closer look at view B of FIG. 27, showing how surfacetension aids in maintaining the deposited material bead at the edge of apart.

FIG. 28 a is another look at view B of FIG. 27 illustrating howadditional beads of material may be attached to an existing overhangingsurface. Additional deposition contours are added serially and Δx iskept small with respect to the bead diameter.

FIG. 29 shows a method of making an overhanging structure by rotatingthe work piece relatively in respect of the deposition head so thefocused laser beam is parallel to a tangent to the surface being built.The deposition head can be rotated in multiple axes to implement therelative movement.

FIG. 30 is an enlarged view C of FIG. 29 showing the relationship of thelaser beam-powder interaction area to the edge of the part which isbeing built.

FIG. 31 is a side-view schematic of the work piece which is the targetof the deposition, showing previously deposited material beads at theedges of the layer to be constructed which act as dams to contain fillmaterial.

FIG. 32 is a side-view schematic of the deposition head using a standardfill process for filling in the deposition layer behind material beadswhich have been placed at the edges as dams, as depicted in FIG. 31.

FIG. 33 is a schematic diagram of an optical fiber laser beam deliverysystem.

FIG. 34 is a perspective view of a laser beam shutter assembly, having aliquid-cooled laser beam “dump.”

FIG. 35 is a perspective view of the laser beam shutter assemblydepicted in FIG. 34 with a top cooling plate removed to reveal the laserbeam “dump” chamber and reflecting beam absorbers.

FIGS. 36 to 40 are side and front elevations and perspective views of amulti-axis deposition head. The head includes an integral powderdelivery system.

FIG. 40 a presents a perspective view of the multi-axis deposition head,illustrating deposition of three-dimensional structure having a curvedsurface. In this example, the head is positioned in three translationaland two rotational axes.

FIG. 41 depicts one of a plurality of powder delivery nozzles of theprior art, which are disposed in a deposition head.

FIG. 42 shows an improved powder delivery nozzle used in the presentinvention.

FIG. 43 reveals a still further improved powder delivery nozzlealternatively used in the present invention.

FIG. 44 depicts schematically the operation of a coaxial gas flow sheathwhich acts as a boundary layer barrier to the entrained powder stream ina powder delivery nozzle. The velocity of the coaxial gas flow and theentrained powder stream are approximately the same.

FIG. 45 is another schematic representation of powder delivery nozzlehaving a coaxial gas sheath and entrained powder stream. In thisillustration, the velocity of the coaxial gas stream is much greaterthan that of the entrained powder stream resulting in mixing of the twostreams. Large de-focusing of the powder stream causes powder to bescattered widely over the deposition surface.

A DETAILED DESCRIPTION OF PREFERRED & ALTERNATIVE EMBODIMENTS

1. Forming Structures Directly from a CAD Solid Model

The present invention comprises apparatus and methods for fabricatingmetallic hardware with exceptional material properties and gooddimensional repeatability. The term “net shape” refers to an articlefabricated to the approximate desired size and features, solid orlatticed, by a process which requires little or no machining. The priorart in this technology has focused on methods to enable the depositionprocess. However, little work has been done on how to best control theprocess to achieve a desired outcome in a solid structure.

The present invention uses the laser-based process to provide users withthe ability to create a net shape or near-net shape, fully dense,metallic object directly from a computer aided design (CAD) solid model.The shapes are created a layer at time. In this Specification and in theclaims that follow, the invention is referred to as a directed materialdeposition (DMD) process. This DMD process has the potential torevolutionize the approach to designing hardware. Presently, designersmust often make compromises in materials selections, and, as a result,achieve a less than optimum solution to a problem. The layer approachused in the material deposition process provides the freedom to varymaterial composition within a single structure. This ability enablescomponents to be engineered a layer at a time to satisfy conflictingmaterial requirements. Currently, the process is capable of producingmetallic objects using stainless steel and nickel-based super alloysthat have nearly a two to three fold increase in strength and withimproved ductility in comparison to conventionally processed materials.Other materials that have been processed include tool steels, copper andtitanium.

The material deposition process of the present invention is functionallysimilar to many of the existing rapid prototyping technology (RPT)methods in that it utilizes a computer rendition of a solid model of anarticle to build an object a layer at a time. Conventionalstereolithography (STL) file format may be used. The file is slicedelectronically into a series of layers that are subsequently used togenerate the motion of the apparatus which deposits each layer ofmaterial. The layers are deposited in a sequential fashion to build anentire part.

A schematic representation of the prior art, laser engineered netshaping process apparatus, is shown in FIG. 1. To begin the fabricationprocess, a metal substrate 19 is used as a base onto which new material15 is deposited. A high power laser 12 is focused by lens 13 onto thesubstrate 19 to create a molten puddle 17 and metal powder 20 isinjected into the puddle 17. The substrate 19 is moved relative to thelaser beam 12 in a controlled fashion to deposit thin metallic lines ofa finite width and height. A stage 16 provides relative motion betweenthe work piece and the deposition head 11 in orthogonal directions andthe focusing lens 13 is moved in the z-axis as the material grows inheight. Lines of material are deposited side by side in the desiredregions to create the pattern for each layer. In this fashion, eachlayer is built up line by line and the entire object evolves, layer bylayer.

Testing was done to prove that a prior technology called LENS.™.processing (“laser engineered net shaping,” a Trade Mark used by theSandia National Laboratories) was viable for direct fabricationapplications. Mechanical testing data from tensile specimens prepared in316 stainless steel and Inconel 625 are given in Table 1: TABLE 1Mechanical test data from LENS ™ manufactured tensile specimens. PlaneOrientation Ultimate Yield with Respect to Strength Strength ElongationTensile Direction (mesh size) (MPa) (MPa) (% in 2.54 cm) 316 SSPerpendicular (−325) 0.793 0.448 66 316 SS Perpendicular 0.793 0.448 51316 SS Parallel (−325) 0.807 0.593 33 316 SS Anneal bar (Standard) 0.5860.241 50 625 Parallel (100/325) 0.931 0.634 38 625 Perpendicular(100/325) 0.931 0.517 37

The ultimate tensile strength and yield strengths of the DMD samples aregiven in mega-Pascals (Mpa). As can be seen from these data, thespecimens produced using the metal deposition process exhibited verygood material properties and, in fact, in all cases the measured yieldstrengths of these samples were significantly better than typicalannealed wrought material. Additionally, the ductility of thesespecimens was as good or better than the annealed wrought material withonly one exception. This improvement in material properties occurred forboth the 316 stainless steel and Inconel 625 alloys. Transmissionelectron microscopy analysis of the 316 stainless steel specimens hasshown that the grain size within the DMD fabricated structures is on theorder of five to ten micrometers (μm) whereas the grain size for theannealed 316 stainless steel is typically around 60 μm. This differencein grain size is believed to be the primary cause of the improvedmaterial properties for the DMD fabricated structures. In addition, thesimultaneous increase in strength and ductility would suggest thatalthough there is undoubtedly residual stress within the DMD fabricatedstructures, it is not sufficiently large to result in degraded materialproperties.

Another problem for many RPT processes is the inability to produceaccurate parts directly from a CAD solid model. Studies were performedthat characterize the DMD process in this area as well. The componentgeometry used in these studies is shown in FIG. 2. The part 28 shown inFIG. 2 represents a simple half-mold that was fabricated for moldingplastic. Measurements made of several areas of this part 28 are includedin Table 2. TABLE 2 Measured physical dimensions of mold halves madeusing LENS ™ process along with statistical results for error andrepeatability. Measurements of Features for NSF Phase I SBIR PartsThunderbird Dimensions (mm) Outside Dimensions (mm) Part Part NumberLength Width Number Wing Span Tail-to-Head 1 76.619 45.009 1 14.68114.478 2 76.670 45.034 2 14.732 14.529 3 76.645 45.034 3 14.656 14.427Avg. Value 76.645 45.027 14.68 914.478 Std. 0.025 0.015 0.038 0.051Deviation Alignment Hole Dimensions Upper Right Hole Upper Left HoleLower Center Hole Part Number X Dim. Y Dim. X Dim. Y Dim. X Dim. Y Dim.1 4.826 4.877 4.890 5.004 3.543 3.607 2 4.826 4.826 4.953 4.902 3.6323.645 3 4.724 4.686 4.775 4.724 3.505 3.556 Avg. Value 4.793 4.796 4.8724.877 3.607 3.602 Std. Dev. 0.058 0.099 0.089 0.142 0.066 0.046

In Table 2, the standard deviation of measurements over several parts isless than 0.142 mm, suggesting that dimensional repeatability of the DMDprocess is very good in the deposition plane. Modification of controlsoftware to account for the finite laser beam width allows this processto very accurately produce parts. A process capable of fabricatinghardware within ±0.127 mm. directly, in metal, will satisfy many currentneeds for direct fabrication applications. It is reasonable to expectthese numbers to approach machine tool accuracy. At this time thedimensional repeatability of the DMD process in the growth or verticaldirection is approximately ±0.381 mm, which is not as good as in thedeposition plane.

DMD technology is clearly valuable for tooling applications. Thisprocess holds the promise of significantly impacting many othermanufacturing areas. Although work to date has focused on producingfully dense metallic structures, modification of existing processparameters allows porous structures to be produced. Both step-functionand gradient-transition interface characteristics between differingmaterials is described below.

Impacted immediately by the DMD technology, are applications where highstrength-to-weight ratio materials are required. For many applications,a tenuous qualification process must be performed prior to substitutionof one material for a second material. Even after qualification,designers are often reluctant to make the transition to a new material.Using DMD technology, composite materials can easily be fabricated fortesting and evaluation.

In developing the DMD process, statistical data from experiments havebeen used extensively by the inventors. These experiments have causedcontrolling relationships between process variables and responsevariables to be identified and defined. From the experimental results,response surface models were developed to optimize the process. Onecritical relationship identified through these experiments was thedeposition layer thickness as a function of certain process parameters.Using the deposition layer thickness as a response variable, both laserirradiance and the velocity of the deposition were identified as keyprocess parameters.

FIG. 3 shows a graph 30 of deposition layer thickness 32 in a z-planevs. laser irradiance (J/sec-cm²) divided by the deposition velocity inan x-y plane (cm/sec) 34. Inspection of this graph 30, shows that thedeposition layer thickness 32 varies approximately linearly with J/cm³34.

The relationship of surface roughness 42 with powder particle size 44 isdisplayed in the chart 40, shown as FIG. 4. For this set of experiments,the average roughness (am) of the surface finish of the depositedmaterial was measured as a response variable while a variety of processvariables including laser power, particle size, particle sizedistribution, etc. were considered as process variables. The chart 40shows that at a given laser power, the surface finish roughness 42 is afunction of the particle size 44, as one might expect. Closer analysisof the graph 40 shows that there is a strong functional dependence ofthe surface finish on laser power. In fact, a statistical analysisindicates a power level of approximately 350 watts achieves the bestfinish independent of the particle size. These relationships have beenused for DMD process optimization in the present invention.

To develop a single system to produce finished parts directly from a CADsolid model, other laser techniques have been evaluated to enhance theDMD process. As an example, laser glazing of a previously depositedlayer has yielded significant improvements in surface finish. Theresults suggest that this method can be applied to achieve the surfacefinish required for tooling and other precision applications. Themeasured surface finish for laser glazing tests is given in Table 3:TABLE 3 Measured surface finish for laser-remelted directed materialdeposition Surface Condition Surface Finish (am) As Deposited 10.97Remelt Condition 1 2.46 Remelt Condition 2 1.88

The measured surface finish for the DMD fabricated part withoutadditional processing is 10.97 am. Applying different processingconditions for the second and third sample demonstrates that surfacefinish can be dramatically improved using a laser glazing technique. Infact, without significant optimization, a surface finish ofapproximately 1.88 am was obtained. Laser glazing is programmable intothe control files, so that the process is not interrupted by removing apartially completed article from the work flow.

1a. Using a Finished Part as a Substrate

In another embodiment of the invention, the substrate may be a generallyor substantially finished part which requires another finish, feature ormodification. In one specific application, this method may be employedto seal up cavities. In another application, this additional depositionstep may be used to provide a hard surface on top of a softer material.In general, this extra deposition can offer a high value-addedmanufacturing process.

1b. Finished Part is Segmented into Different Features

In another embodiment of the invention, the component being fabricatedis segmented into different features that are built in a sequentialfashion by determining the optimum build direction for each segmentprior to building the complete component.

2. Controlling the Microstructure of Materials Formed by DirectedMaterial Deposition

Referring again to FIG. 1, it shows the directed material depositionapparatus 10 of the prior art. A collimated laser beam 12 is focusedonto a substrate 19 and powdered material 14 is then injected into thedeposition spot. The powder 14 streams come into the deposition area 20and are melted by the laser beam which is focused by lens 13. Initiallythe deposition begins at the surface of the substrate at the depositionspot on the substrate 19. As the fabrication progresses, the depositedmaterial layers 15 are built into the desired shape.

FIG. 1 a shows a layer of material 15, having a thickness Δt, depositedon top of a substrate 19 or substructure. Material properties such astensile strength, toughness, ductility, etc. may be engineered into thematerial layer 15 using a laser-exposure factor (E), defined as:$\begin{matrix}{E = {a{\frac{p}{v}.}}} & {{Equation}\quad(1)}\end{matrix}$

Constant a includes the focused laser spot diameter and materialconstants. Variable p is the laser power in Joules per second, and v isthe velocity in centimeters per second, of the deposition 15 relative tothe surface of the substrate 19 or substructure. The exposure parameterE is a measure of energy input and thus has an effect on thesolidification or quench rate of the deposited material 15. Thickness Δtof the layer is critical to the control of material microstructure. Itaffects the quench rate, but it also affects the thermal gradientcreated in the deposited structure. If thickness Δt is preciselycontrolled along with solidification rate, then the materialmicrostructure within a DMD structure can be controlled. Knowing thethermal gradient and how to vary it allows one of ordinary skill in theart to precisely control the microstructure of the deposited material.Production of articles having directional solidification and evensingle-crystal structure is enabled. See the discussion below inSections 5 in respect of forming structures from multiple materials.

Substrate temperature biasing helps when one wishes to make parts havingsingle-crystal growth. This technique is described in more detail below.

FIG. 4 a depicts a tensile stress versus exposure graph 48 thatdemonstrates how material strength varies with the exposure parameter E.In the graph, 0.2% yield strength 47 of 316 stainless steel is plottedagainst values of the laser-exposure factor 49. A regression line drawnthrough the data points shows that the 0.2% yield strength 47 of thetest material, declined approximately 0.030 kilopounds (Kips) per squareinch, per unit of laser-exposure factor 49.

3. Substrate Heating for Producing Parts Having Accurate Dimensions

FIG. 5 reveals a side view of three different substrate pieces 50, 52,54 that were exposed, in an actual experiment on H13 tool steel, to thelaser beam 12. Different biasing temperatures were applied to thesubstrates 50, 52, 54. The first substrate 50 was not preheated beforethe laser beam impinged on its upper surface 51. Because the upper andlower surfaces cooled differentially, the substrate 50 has deformed 56.A second substrate 52 was preheated to 100 degrees centigrade (° C.)before the laser beam melted the upper surface 53. The substrate 52 alsosuffered deformation 56 a, but considerably less than in the first case.A third substrate 54 was preheated to 200° C. No deformation is seen,even though the upper surface 55 was subjected to the same meltingconditions as the other two substrates 50, 52.

The substrates 50, 52, 54 were first ground flat. On the upper surface51, 53, 55 of each substrate 50, 52, 54 was deposited two one inch byfour inch patterns of material. Each of the substrates 50, 52, 54 wasmeasured for flatness prior to beginning the tests. The first patterndeposited was one layer thick and the second pattern was 10 layersthick. For substrate 50 which was at room temperature when thedeposition was made, a distortion 56 or change of flatness of 0.012inches was observed. For substrate 52, preheated to 100° C., adistortion 56 a or change of flatness of 0.008″ was observed. Forsubstrate 52, preheated to 200° C., no measurable change in flatness wasdetected. An additional test was made preheating a substrate to 300° C.bias temperature. No measurable distortion was observed.

FIG. 6 shows an embodiment 70 of the directed material depositionapparatus in which heating is applied to the substrate 19 and deposition15. A heat lamp 72 or other radiant source such as a laser directsradiant energy 74 to the work area 15, 19. A thermal monitoring device76 such as an optical pyrometer is utilized to control the temperatureof the work area 15, 19.

FIG. 7 reveals another heating method 80 in which a heated platen 81 ispart of the x-y axis movable stage. The platen 81 provides heat to thesubstrate 19 and deposition 15 during processing. A temperature sensor86 is attached to the substrate 15. Heating elements 82 are built intothe platen 81. A platen temperature sensor 84 monitors platentemperature.

Of course, the heating methods described above are only examples. Othermethods of heating the work are possible, such as an inductive heatingsource or a furnace surrounding the work.

FIG. 8 is a chart of temperature versus time 90 and depicts a profile oftemperature applied to a substrate 19. The temperature of the substrate19 is controlled before, during and after the build sequence to insurethat the optimum material properties are obtained in the depositedmaterial. The thermal profile 90 shown in FIG. 8 begins at roomtemperature. The temperature is then raised in a controlled ramp 95 upto the processing temperature. A constant temperature 96 is maintainedduring material deposition, and a controlled ramp 97 down in temperatureis programmed during the time the material is cooling. This insures thecorrect microstructure of the material is achieved when the articlecools.

FIG. 9 depicts the difference between a material deposition with heating15 applied during processing and a material deposition without heating15 a. In the non-heating case, the top surface of the deposit 15 a isflat but the substrate 19 is distorted. Because of the distortion of thesubstrate 19 and deposition 15 without heating, it is very difficult tocontrol the dimensions of the deposition 15 both horizontally andvertically. However, when heating by use of apparatus shown in FIG. 7 or8, the substrate 19 and deposition 15 have no detectable distortion andthe dimensions of the deposited article 15 are closely controlled.

An alternate profile 110 of heating applied to the deposition 15 duringfabrication is depicted in FIG. 10. As in the earlier-described profile90, the cycle begins from room temperature with a controlled ramp 112 upbefore deposition and a steady soak 114 during deposition and acontrolled ramp 117 down in temperature after deposition. In thisprofile 110, steps 118, 120, 122 are added to further improve theproperties of the deposited material 15. The part is not allowed to coolto room temperature prior to completing the entire thermal cycle 110.

4. Depositions Using Several Materials

FIG. 11 shows schematically the directed material deposition system 123for fabrication with at least two different materials, and having meansto preheat the substrate 19 and the material layers 15 thereon. Thelaser 124 projects a beam 125 through the powder deposition head 11 ontothe substrate 19 and subsequently the material layers 15. The substrate19 is mounted on an x-y axis positioning stage 16 which contains heatingand heat control apparatus. The positioning stage 16 moves the substrate19 in a plane under the focused laser beam 125 a. Two different powderfeed units 126, 127 supply the powder deposition head 11. A z-axispositioning stage 18 raises or lowers the focal point of the focusedlaser beam 125 a as the deposition grows. An enclosure 128 controls theatmosphere in the process area. The atmosphere is usually desired to beinert, but could be a reducing or oxidizing atmosphere.

A computer 129 and monitor 129 a control the deposition process fromstored data and CAD control files.

5. Forming Structures from Multiple Materials

Adaptation of the DMD apparatus 123 and methods have been applied to theproblem of creating articles comprised of multiple materials in order totake advantage of the properties of each material. Multiple-materialstructures have been made by other processes, however, in the prior artthere is no useful method of fabricating these structures directly froma computer rendering of an object. Prior art CAD systems and associatedsoftware only describe an article by the surfaces bounding the object.Thus, they are not effective to define the regions of gradient materialsdirectly from computer files in those CAD systems.

In creating these structures using DMD techniques, several technicalhurdles were overcome. These include: material compatibility;transitions from one material to another material; and definition of themultiple-material structure so that a simple computer controlled machinemay automatically produce such a structure.

Instant change of feedstock materials, delivered from the powder feedunits 126, 127 in a controlled manner, is another key requirement forthe production of three-dimensional, gradient material structures. Knownpowder feed systems do not meet this requirement.

The invention includes hardware to control powder flow with littlehesitation. It also provides a method for controlling the materialcomposition, and thus the material characteristics, within a multiplematerial structure directly from computer renderings of solid models ofthe desired component. This method functions both with the industryaccepted stereolithography (STL) file format as well as with other solidmodel file formats. The concept allows designers to create multiplematerial structures that are functionally graded, have abrupttransitions, or both. In addition, this invention provides a method tocreate these structures using the current solid model renderings thatonly define the surfaces of a model.

The development of solid free form (SFF) technologies, such asstereolithography, has created an increasing interest in creatingfunctionally graded materials directly from a computer-rendered object.Once an object's shape is defined and the regions identified within theobject where different materials are to be deposited, the object canthen be broken down into a series of solid models that represent each ofthe different material regions.

FIG. 12 is a perspective sketch illustrating the concept 130 ofcapturing a solid model made of one material within a solid model madeof a different material by means of the present invention. FIG. 12presents a simple case for illustration purposes in which a block 132 ofa first material is located within a second larger block 134 composed ofa second material. The larger block 134 contains a cavity at its centerwhich is the desired shape of the second block 132.

FIG. 13 is a cross-sectional view of the composite, two-materialsstructure 130 seen along section A-A of FIG. 12. In this structure 130,the outer block 134 is shown as being formed by layered depositions 138made horizontally. The inner block 132 is seen as formed by layereddepositions following the hatching 142 along a 45 degree angle. There isa region 136 between the inner block 132 and the outer block 134 whichis to composed of both materials and is graded from outer block 134material beginning at a surface interface 140 in the large block 134 andcontinuing to a surface interface 144 of the inner block 132.

In this example, the multiple material structure is defined from twosolid models. FIGS. 13 and 14 illustrate these two solid models 141, 146in cross-sectional view looking along section A-A of FIG. 12. The solidmodel 141 representing a first material is bounded by the exterioroutline 143 and interior outline 144 of outer block 134. In FIG. 14, thesolid model 146 representing a second material is “exploded” for easiervisualization of the two separate models 141, 146. The solid model isbounded by the outline 140 and forms the inner block 132 and thecomposite, graded material zone 136. The regions defined by each of thesolid models include the region 136 where the composite of the twomaterials is graded. By defining each of the solid models 141, 146 ascontaining the region where the desired amount of first material andsecond material will exist, the DMD apparatus 123 is programmed todeposit each of the materials in the correct proportion.

Using conventional methods, each of the solid models 141, 146 can beelectronically sliced into layers, from which programming the solidobject is fabricated. For a typical solid free-form method, a series ofcontours 140, 143 and hatch-fill lines 138, 142 are used to deposit thestructure a layer at a time. The contour information is used to definethe boundaries 140, 143, 144 of the object and the hatch-fill lines 138,142 are used to fill the region within the bounding surfaces. It is onlynecessary now to define how the material is to be graded within theoverlap region. This is input to the computer as a function of thecoordinate axes, f(x,y,z). If it is assumed that the solid model slicesare taken in steps along the z principal axes, then the grading becomesa function of the x and y coordinates on any given layer.

A preferred method of implementing this strategy is to define each ofthe solid models 141, 146 as independent entities and to electronicallyslice each of these models 141, 146 into layers as is typical for asolid free form method. When dimensions of the first solid model 146 andthe second solid model 141 allow, these two “sliced” objects arerecombined on a layer-by-layer basis. The slice information can becompared in the computer in order to define the single-materialboundaries as well as the hatching information for the graded materialregion. The combined-slice files can then be used to directly drive aDMD apparatus 123 where the composition can be varied directly by thecomputer 129.

Referring again to FIG. 11, the directed material deposition process iscarried out inside a sealed chamber 128, although this is not strictlyrequired. The laser 124 generates a beam 125 which is focused to heatsimultaneously a deposition substrate 19 and powder feedstock material126, 127 that is supplied to the beam/powder interaction region 20. Thelaser beam 125 is focused 125 a to provide an area of high irradiance 17at or near the surface on which the deposition is to occur. The areaincluding the focused laser beam 125 a and initially, the depositionsubstrate 19 surface comprises the deposition region. The depositionregion changes with time, thus it is not necessary for the deposition toalways correspond to the surface of the deposition substrate 19. As thedeposited material layers 15 build up, the deposition region can bemoved far away from the original deposition substrate 19 surface. At ornear the deposition region, the powder feedstock material 126, 127intersects the focused laser beam 125 a and becomes molten to create anew layer of material 15 on an existing substrate 19.

As additional new material is supplied to the deposition region, thesubstrate 19 on which the deposition 15 is occurring is scanned in afashion predetermined by computer programming such that a specificpattern is created. This pattern defines the region where the materialis deposited to create one layer of an object that is comprised of aseries of lines. The relative position between the focused laser beam125 a and the powder feedstock material 126, 127 is fixed with respectto each other during the deposition process. However, relative motionbetween the deposition substrate 19, which rests on the orthogonal, x-ypositioning stages 16, and the beam/powder interaction zone 20 isprovided to allow desired patterns of materials to be deposited. Throughthis motion, materials are deposited to form solid objects a layer at atime, to provide a surface-coating layer for enhanced surfaceproperties, and to deposit certain materials in a specific pattern toproduce the object configurations described above and below. Computercontrolled motion of the x-y stages provides one means for controllingthe relative motion between the deposition substrate 19 and thebeam/powder interaction zone 20. The computer control method ispreferred to control this motion since the process is driven directly bythe solid model data contained within the CAD files. Persons skilled inthe art will appreciate that alternatively, the stage 16 can bestationary and the deposition head 11 moved in relation thereto.Movement of the deposition head in multiple axes, for example up to fiveaxes, offers advantages of flexibility over the conventional x-y planepositioning, for producing overhangs and other shapes.

The present invention offers a deposition process that uses more thanthree axes of motion such that the part build axis can be varied duringthe process to allow unsupported overhangs to be built. In analternative deposition process, the additional axes of motion may beused to fabricate outer surfaces that are unsupported by directing thedeposition beam such that it is substantially tangent to the overhangsurface. In one embodiment of the invention, these additional axes ofmotion are provided by a multi-axes deposition head 480.

5a. Feedstock Rapid-Action Powder Metering Valve

Rapid-action metering of powder feedstock flow is controlled by a spoolvalve assembly 149 such as shown in schematic form in FIG. 14 a. Theprocess of proportional powder flow control implemented with the use ofthe valve assembly 149 is depicted schematically in FIG. 14 b. Rapidresponse to changing mass-flow requirements for powder material deliveryis accomplished by using a plenum to mix powder-rich and powder-free gasstreams. No stagnant flow condition can be permitted in the system oncepowder is “fluidized” in a carrier gas stream. Downstream of the mixingplenum a flow diverter 149 directs part of the powder-rich stream Gp andpart of the powder-free stream G into a powder material delivery path154. The volumetric flow rate of the carrier gas into each inlet 150,151 is separately controlled and maintained. The flow diverters 158 arecontrolled proportionally so that the total volumetric flow rate ofpowder material is constant. The powder mass flow rate in the deliverypath 154 to the work piece can be varied quickly from no powder to thetotal mass flow available in the powder-rich stream Gp. Waste gas andpowder 150 a are re-circulated. Waste gas 151 b is reclaimed.

A flow of powder, entrained in a gas vehicle Gp such as argon or helium,is introduced into a valve body 152. A flow of gas only G enters thevalve body 152 through inlet 151. A plunger 156 in which diverterpassages 158 are formed, slides in and out of the body 152. With theplunger 156 in the position shown, the gas with entrained powder PG isseparated into two flows 150 a, 150 b through the diverter passages 158.The gas G entering through inlet 151 is also separated into two flows151 a, 151 b. The flow through each of the diverter passages 158 isproportional to the cross-sectional area of each passage 158 which ispresented to the inlets 150, 151. Therefore, depending on valveposition, a proportional amount of powder and gas 150 b, 151 a flows tothe work through the diverter passages 158 and a first valve outlet 154.Waste powder and gas 150 a flow from a second valve outlet 153.Remaining gas 151 b flows from a third valve outlet 155. The residualgas flow 151 b from the third outlet 155 is combined with the wastepowder and gas flow 150 a downstream of the valve. This ensures aconstant flow of gas through the system while the valve is in any openposition, but varies the flow of powder to the work according to plunger156 position. Powder and gas 150 b, 151 a are delivered to thedeposition apparatus. Waste powder and gas 150 a, 151 b are returned tostorage.

Rapid variation of the flow of powder and gas Gp occurs when the plunger156 is partially withdrawn from the valve body 152 and the diverterpassages 158 are no longer fully presented to the to the inlets 150,151. The flow paths 153, 154, 155 are quickly altered without stoppingthe motion of the powder particles. The plunger 156 is positioned undercomputer control in accordance with the CAD files used to control thedeposition 15. A mass flow sensor 159 measures powder flow rate in realtime. The sensor 159 output is used for closed-loop control of powderflow 150 b, 151 a. As variations in powder flow occur, the sensorsignals for the powder required for the process.

One embodiment of the invention utilizes a fast acting valve for powerflow control comprising at least two inlet ports and three outlet ports.A powder and a gas flow into the one outlet 150, and impinge onto theseparating unit 156 where the powder and gas stream are separated intotwo streams 150 a, and 150 b. The separated streams are then directedout of the valve into tubes 153, 154. Gas input in tube 151 is alsosimultaneously separated into two streams 151 a and 151 b, and directedinto tubes 154 and 155 such that it combines with the two powder streamsto provide additional gas flow. This feature prevents the powder streamsfrom slowing down this additional gas is required to maintain theminimum powder velocity to avoid having powder settle out of the gasstream.

Another embodiment of the invention, a spool valve for controllingpowder flow rate may be employed. The spool valve comprises a gas andpowder inlet 150; a separator 156 and two outlet tubes. The second gasinlet is provided to make up for the flow reduced caused by theseparator 156.

5b. Volumetric Powder Feed Unit

FIG. 15 is a perspective view of a volumetric powder feed unit 170. FIG.16 is a perspective view of the same unit, seen in the direction of viewB-B of FIG. 15. The unit 170 allows a user to achieve extremely low flowrates with a variety of powder materials 185. FIG. 16 a is a perspectiveview of the powder feed disk 179 and wiper assembly 184, alone (i.e.,removed from the powder transfer chamber 178), revealing a series ofpowder feed receptacles 181, disposed circumferentially around the faceof the powder feed disk 179, which pick up powder from the supply pile185. The powder feed receptacles 181 are formed by piercing the powderfeed disk 179, typically by drilling, at a radial distance from the axisof disk rotation 183.

The powder feeder design is a marked improvement over current disk-stylepowder feeders in which the disk typically is buried in powder. In thepresent invention, powder flow from a reservoir 172 to a transferchamber 178 is limited by the angle of repose of the powder feedstock185, preventing the disk 179 from being overwhelmed and clogged withpowder 185. The present invention is insensitive to variations in flowrate of the gas 187 which transports the powder 185 to the depositionhead. The spacing between the feed disk 179 and wipers 184 which removepowder from the disk can be greater than in prior art designs withoutlosing control of powder metering. This promotes much less wear on thewipers 184 and substantially improves the life of the powder feed unit170.

During powder feeder 170 operation, powder feedstock 185 from the powderreservoir 172 enters the powder transfer chamber 178 through feed tube190. The powder 185 necessarily forms a heap that limits flow into thepowder transfer chamber 178 but presents a constant source of powder 185to the feed disk 179. The powder 185 partially covers the powder feeddisk 179 which is disposed perpendicular to the axis of rotation of thefeed disk 179 so a portion of the disk 179 and a portion of powderreceptacles 181 are immersed in the feedstock powder 185. The powderfeed disk 179, is driven by a motor 180 and motor controller 182. Theseries of feed receptacles 181 in the face of the disk 179 bring acontrolled volume of powder 185 to the wiper assembly 184. Gas 187entering under pressure through a gas inlet 186 clears the powderreceptacles 181 of powder 185 by blowing it into a powder-and-gas outlet188. From there, the powder 185, entrained in gas 187 is transported tothe deposition zone 15.

To facilitate the transport of powder 185 from the powder mound to thewiper assembly 184, the powder feed disk 179 is partially immersed inthe powder mound as it is rotated by the motor 180. The receptacles 181in the disk 179 fill with powder 185. As the disk 179 rotates, only thepowder in the disk receptacles 181 remains with the disk 179 as it exitsthe powder 185 mound. When the disk holes pass the wiper assembly 184,powder transport gas 187 “fluidizes” the powder 185 and entrains it in agas stream 174 that is carried to the deposition area for use in thedirected material deposition process. The transport gas is typically aninert gas such as argon or helium, although other gases such as nitrogencan be used in order to obtain special properties in the depositedmaterial 15.

Another optional feature employs a tube on the bottom of the hopperwhich extends into the horizontal chamber 178. The powder passingthrough the extended tube can form a powder heap in the horizontalchamber 175 that partially covers the vertical powder feed wheel.

The powder feed wheel may be configured to rotate through the powderheap so that the holes in the powder feed wheel fill with powder that iscarried past the gas 187 inlet or outlets. This arrangement renders thepowder. This feature of the powder feed unit allows close tolerancesbetween the powder feed wheel and the gas inlet and outlet wipers to bemaintained, while keeping the powder largely away from these surfaces.As a result, these surfaces are not covered with powder continuously,and so the reliability is increased substantially.

The graph of FIG. 16 b plots average flow rate for 316 stainless steelpowder versus powder feed disk rotational velocity (RPM) for three testconditions, showing the performance of the powder feeder. The flow rate200 can be varied approximately linearly from about 0.1 grams per minuteto about 30 grams per minute depending directly on the rotational speedof the powder feed disk 179. The powder feeder 170 is a neededimprovement to facilitate fabrication of gradient material structures.

5c. Joining Dissimilar Metals in DMD Process

When joining dissimilar metals in a DMD process, it is often necessaryto place a “buttering” layer of one or more materials between the twodissimilar metals being joined. Buttering is a method that depositsmetallurgically compatible metal on one more surfaces of the dissimilarmetals to be joined. The buttering layers prevent coalescence of thedissimilar metals and provide a transitional region between them,because of, among other things, material incompatibility. An example ofone preferred method of this process is shown in FIG. 16 c.

In FIG. 16 c, a substrate 210 is first manufactured or deposited from a“base” material. Buttering layers 212 & 214 of a first and secondtransitional material are next deposited over the first base material210. When the transitional layers 212 & 214 are completed, a second basematerial 216 is deposited on top of the transitional layers 212 & 214.It should be appreciated that one or more buttering layers 212 & 214maybe required depending on the properties of the dissimilar metals tobe joined. As examples, some practical combinations are nickel as abuttering layer between copper alloys and steel, 309 or 310 stainlesssteel as a buttering layer when joining stainless steel to a carbon orlow alloy steel, and 309 stainless steel as a buttering layer between aferritic and austenitic stainless steel.

FIG. 16 c depicts flat material layers, but it should be appreciatedthat these layers may also be contoured in several directions. FIGS. 17through 23, discussed below, illustrate the invention's ability to formsurfaces having complex contours.

6. Forming Cooling Channels for Thermal Control of Three-DimensionalArticles

Directed material deposition processes allow complex components to befabricated efficiently in small lot sizes to meet the stringentrequirements of the rapidly changing manufacturing environment. Thepresent invention creates within a solid article, internal featuresusing direct material deposition techniques coupled with alayer-by-layer manufacturing. These internal features provide thermalcontrol of complex shapes, in ways not previously available. Oneimportant use for this invention is providing high efficiency coolingfor injection mold tooling. The technology provides the ability tocreate an isothermal surface as well as produce thermal gradients withinthe part for controlled cooling.

The following discussion discloses features that are obtainable in anarticle by using direct material deposition manufacturing techniquesincluding material sintering techniques. The development of precisematerial deposition processes provides the ability to create structuresand material combinations that were previously not capable of beingmanufactured easily. Traditional methods cannot be used easily formanufacturing these internal geometries and multiple material structuresthat are completely enclosed in a solid body. Embedded structuresforming conformal cooling channels support rapid and uniform cooling ofmany complex shapes. The shapes may have irregular internal or externalgeometry.

7. Thermal Management within Solid Structures

There are often compromises that must be made to work within theconstraints of the physical environment. Compromises in the thermalmanagement within solid structures have often been required. Forexample, in tooling there are often conflicting requirements forlong-lifetime tool and one with efficient cooling properties. For theseapplications, designers will typically use a form of tool steel whichcan be hardened and which will provide a very good wear surface.However, the thermal conductivity of tool steels in general isrelatively poor. Therefore, the cooling cycle time is compromised infavor of long tool life. The invention described herein allows thesenormally conflicting requirements to be simultaneously satisfied. Inaddition, methods of the present invention provide the ability tofashion the structures beneath the surface of a component to tailor thethermal characteristics of the structure. Thermal characteristics withina structure can be manipulated to control the rate at which a componentis heated and cooled.

The opportunity to embed features such as passages, chambers andmultiple material structures is provided with the present invention. Asan example, structures are shown in FIGS. 17 through 23 in whichpassages and chambers are integrally formed. The passages and chamberscan be empty, or filled with a circulating coolant liquid. They may alsobe filled with another material that performs a function such asincreasing or decreasing the rate of cooling or heating in thestructure. The passages and chambers may be interconnected to provideuniform thermal control or several passages or chambers can exist withina component that are not interconnected to provide localized thermalmanagement. The structures may be actively or passively temperaturecontrolled. Active control is accomplished by flowing a fluid coolantmedium through the passages and chambers. Passive temperature control isachieved by combining the basic component material with other materialsthat locally affect the thermal gradients in particular regions of thecomponent.

A schematic diagram of one preferred embodiment of this invention isgiven in FIG. 17. Cooling passages 252 which conform to the shape of amold cavity 254 are integral with the mold block 256. For clarity, themold block 256 has been cross-sectioned through a mid-plane 258,exposing the internal cooling passages 252 and support fin structures259. The arbitrarily shaped injection mold block 256, is the base thathouses the mold cavity 254 and the conformed cooling passages 252. Thepassages 252 follow the contour of the surface they lie beneath at aprescribed distance beneath the surface. The conformal cooling passages252 are designed to follow the surface of the mold cavity at prescribeddistances, determined by the desired cooling balance of the mold cavity.

The present invention produces injection molds having rapid, uniformcooling. The conformal cooling systems are integrated into the moldinserts 256 fabricated by directed material deposition techniques.Cooling passages 252 are fabricated using a DMD system 123. When usingDMD techniques, passage width can be chosen such that no supportmaterial is needed and the passages will remain open cavities that arecompletely enclosed in the mold base 256. The conformal cooling channels252 provide uniform support for the mold cavity 254 as well as increasethe surface area of the cooling channel surfaces 259.

The embedded features 252, 259 are produced in the three-dimensionalmold insert structure 256 by feeding one or more separate materialfeedstock 126, 127 into the directed material deposition process 123 anddepositing the melted feedstock 126, 127 onto a substrate 19. Thedeposition is made in a manner depicted in FIGS. 12 through 14 anddescribed above, according to computerized files of solid models of theelements of the completed article. In addition to external contours, thesolid-model computer files describe regions of each separate material,regions of a composite of the materials and regions of voids in eachlayer or “slice.” The steps are repeated a sufficient number of times inlayer-by-layer patterns, defined by “slices” of the solid models, tocreate the three dimensional structure 156 having the geometric detailsdepicted in FIGS. 17 and 18. It should be appreciated that these stepscan produce nearly any other shape that can be imagined.

A finned structure 252 as shown in FIG. 17 provides several advantagesover structures that can be produced using existing methods. Typically,cooling passages are drilled into a structure. However, the circularcross-section of the drilled passages present a minimum surface area incontact with the thermally conductive medium. Finned structures 252 canprovide an order of magnitude increase in surface area. A finnedstructure 252 provides support for the exposed surface 254. This iscritical for applications such as injection molding of plastic partswhere the pressure can be on the order of 5000 pounds per square inch.One of the factors that influence the heat transfer rate of a structureis thermal conductivity of the material. A second is the efficiency atwhich the energy is transferred to the heat conducting medium. Uniformlydistributing fins 259 beneath the surface of the component compensatesfor poor thermal conductivity of its materials.

FIG. 18 is a perspective view of a full mold block 256. Shown here areinlet port 260 and outlet port 262 for the flow of a coolant mediumthrough the mold conformal cooling passages 252. In this application,cooling passages 252 that conform to the shape of the mold cavity areprecisely located. The cooling passages 252 can be connected to otherpassages through the ports 260, 262. The passages 252 can be designedfor equal and uniform flow of coolant, or whatever flow is optimum inthe circumstances.

These structures offer another advantage in thermal management offabricated articles. They can be designed to create a constant pressureand uniform flow of the coolant medium across the entire structure. FIG.19 is a cross-sectional view of a solid, rectangular article 270,showing the internal cooling passages 276 and inlets 272, 274 madeintegral with the article 270. Although coolant inlet and outlet ports272, 274 can be introduced into the part from almost any location, theirrespective location to the inlet and outlet of the cooling channels 276plays a significant role in obtaining uniform cooling in thesestructures. The cooling channels 276 are terminated in reservoir-likefeatures 278. The inlet 272 to a first reservoir 278 is at one end andthe outlet 274 is at the end of a second reservoir 279. A constantpressure drop and uniform flow through the structure is thus provided.This is similar to the structure of a cross-flow style radiator used inan automobile. Of course, other structures used for flow control canalso be formed by DMD processes.

The DMD processes provide the unique ability to deposit a plurality ofmaterials within a single build layer. This provides yet anotheradvantage of fabricating structures with integral thermal managementfeatures. In many structures, the control of the temperature by activemeans is not possible. There may be no way to embed cooling passages 252within a low thermal conductivity material structure 256 to facilitateheat transfer. In that case, the structure is fabricated such that theregion beneath the surface is composed of a high thermal conductivitymaterial. A technique similar to that depicted in FIGS. 12 through 14and described above is used. High thermal conductivity materialdeposited in the cavities of lower thermal conductivity materialprovides a solid structure that acts as a heat pipe. The high thermalconductivity material is placed in contact with a heat exchange mediumwhich provides a means to quickly cool adjacent lower thermalconductivity material.

FIG. 20 is a schematic of an alternate embodiment. It is across-sectional view of a cylindrical article 280 of random lengthhaving integral cooling passages 282. The structure's geometry increasescooling surface area by a significant amount. The internal coolingstructure can vary in cross section and direction.

FIG. 21 is a cross-sectional view of a cylindrical object with complexgeometries of separate cooling passages fabricated into the component.The view depicts an cylindrical shape 286 with multiple independentloops of cooling passages 288 and a plurality of cooling channels 289having a common reservoir. A plurality of cooling passages 288, 289 canbe incorporated for separate cooling media.

FIG. 22 is a perspective view of a solid, curved object 290 having thecooling passages 292 following the contour of the outer shape of theobject 290. A person of ordinary skill in the art will appreciate thatcooling passages 292 of very complex geometry can be incorporated intoan arbitrarily curved shape 290. The method of the present invention,however, is not limited to heat exchanger technology in solid bodies.

FIG. 23 is a perspective view of an airfoil shape 300, such as a turbineblade, with cooling channels fabricated integrally within the airfoil.The figure illustrates incorporation of cooling channels 302 into anirregular, arbitrary shape having length, twist and curvature. Theadvantage of fabrication with the present invention over extruded shapeswhich can only have a constant cross-section should be clear.

8. Smart Substrates for Reduced Fabrication Time

The present invention is clearly useful for construction of articleswith internal spaces which cannot be reached easily from the surfaces ofthe article for machining. Of course, there is no point in fabricating aportion of an article which can be made by using conventional meanseffectively. But certain “smart” substrates can be made by deposition,used as a starting point for manufacturing the whole article and canbecome part of the final structure. FIG. 24 is a perspective view ofsuch a substrate 310 a in which the outside envelope 312 and insidecavities 314 have been partially constructed by deposition using methodsalready described above. In FIG. 25, the upper surfaces 316 of thesubstrate 310 b have been approximately three-quarters deposited. FIG.26 reveals the completed substrate 310, before any additional,conventional machining.

Yet another embodiment of “smart” substrate is revealed in the thermalmanagement structure of FIG. 26 a. The lattice structure 318 is anembedded structure in which the volume of deposited material isminimized but the design offers sufficient support for many differentapplications. This structure allows the tubular structure 319 betweenthe surfaces 320 to be flooded with a liquid or gas medium providinggood energy-transfer efficiency between the surface 320 and the tubularstructure 319. Such a device for providing thermal management ofsurfaces 320 allows an end user to control temperatures of the structureat a surface 320.

In FIGS. 26 b and 26 c, another structure 322 is illustrated in whichthermal management structures are embedded beneath the surface 323 usingthe DMD process. This structure 322, shows particularly a tool forplastic injection molding in which the cooling channels 324 within thestructure 322 conform to the shape of the molding surface 325. Unlikethe finned structures shown in FIGS. 17 through 23, the channels herehave a circular cross-section. Further enhancing the ability to controlthe temperature of a structure at its surface, cooling structures canalternatively comprise embedded materials of different thermalconductivity from the surface material. For example, copper can be usedas an embedded material of high thermal conductivity.

9. Fabricating Unsupported Structures

A combination of methods is used to build three-dimensional, gradedmaterial structures. A problem of construction is creating overhangingedges which may occur in cavities within a structure. FIGS. 27 and 28illustrate one preferred method of producing an unsupported overhang 346in a structure 15 using three-axis positioning. The focused laser beam340 is moved a distance Δx over the edge of a previously depositedsurface 15 and a bead of material 344 is deposited. The distance Δx istypically less than ½ of the focused laser beam diameter 17. At thisdistance Δx, surface tension of the melted material 342 aids inmaintaining the edge, thus allowing a slight overhang 346. By repeatingthis deposition several times in one layer 348, an angle of the overhang346 of approximately 60 degrees can be achieved. After the over hangingedge 346 bead 344 and other edge beads 344 are deposited, material isfilled in to complete the layer 348.

FIG. 28 a shows how additional beads of material may be attached to anexisting overhanging surface 346. By defining the overhanging surface346 as a series of contours that incrementally move outward, away from asolid structure 15, several beads 345 of material may be added to astructure to extend the build over an unsupported region. A second beadof material 345 is deposited to the first edge bead 344 using a multiplecontouring method. The overhanging surface is extended into a regionwhere there is no underlying support for the bead. The method provides a“virtual” support for the overhanging build.

In an alternative embodiment, the multi-axis capability of the inventionis used to deposit the overhanging surfaces 344, and then the filledregions are filled 348 by the deposition beam, which is directed towardsthe build surface in a direction normal to the substrate surface.

In another alternative embodiment, the plane of deposition is rotated inrespect of the work piece 15 as shown in FIGS. 29 and 30 so the focusedlaser beam 340 is parallel to a tangent 343 to the surface which isbeing built. When the edge beads 344 have been deposited as in FIG. 31,the part can be reoriented with the deposition layer 348 normal to thelaser beam 340 axis as seen in FIG. 32. The layer 348 is filled in, asbefore.

Note that either the part 15 or the laser deposition head 14 can beadjusted to accomplish parallelism of the laser beam 340 axis with thetangent 343 to the surface of the deposition 15. In fabricating certainconfigurations of structures, it is easier to tilt and rotate thedeposition head axes than those of the part. The present invention,therefore, includes a deposition head which deposits materials indirections other than downward along the z-axis.

10. Protecting the Fiber Optic which Delivers Laser Power to the Work

Work with known systems 10 in the field has shown that catastrophicfailure of a fiber optic used to deliver laser energy to the depositionsurface 15 can occur because of the effect of reflected laser energy onthe optical fiber. The present invention includes a laser beam deliverysystem which eliminates this problem by imaging both specular anddiffuse reflections from a laser beam emanating from the work area 17 onan area of surface that is a distance from the fiber optic face.

The laser beam delivery system 420, depicted in FIG. 33, provides alaser beam 436 from a preferred Neodymium YAG laser. The beam 436emerges from an optical fiber 430 and is focused on a spot 17 on thesurface of the work piece 15. The beam 436 is reflected to the workpiece 15 at an approximate right angle by a folding mirror 438. Afterthe diverging laser beam 436 leaves the optical fiber 430, it iscollimated by lens 433. The collimated beam 436 is then focused by aconvex lens 434 to achieve the high power density required to meltmaterial at the work piece surface 15.

In prior fiber delivery systems, off-axis reflections result when raysof an unfocused laser beam reflect from a folding mirror used in theoptical system, at an angle other than 45°. In the present invention,because the beam is focused before it strikes the mirror 438, the offaxis reflections do not occur. While the reflected beam 439 has a smallaberration, it only serves to spread out the beam energy at the beamimage 17 on the deposition surface 15.

Typically, the folding mirror is positioned at 450 to the axis 440 ofthe beam 436 and reflects the focused beam 436 a normal to the workpiece surface 15. When the laser beam 436 a is sharply focused on thedeposition surface, any reflected light travels along the reverse path.A reflected beam 439 is incident on the folding mirror 438 and isdirected through the focusing lens 434 in a reverse direction. Thefocusing lens 434 now collimates the reflected laser energy and thecollimating lens 433 focuses the reflected beam 439 onto the opticalfiber 430. Since there is generally some tolerance associated with themirror 438 mounting, the beam 436 may not always be coupled directlyback normal to the optical fiber face. If coupling should occur, some ofthe reflected laser light 439 leaks out of the fiber 430 and for a shorttime no serious heating results. During the powder deposition process,however, the operating time is long enough that the optical fiber 430can be damaged by the additional heat of the reflected laser beam 439.

To solve this problem, the reflected laser beam 439 is deliberatelyimaged elsewhere than on the optical fiber 430. By tilting the foldingmirror slightly from 45° to the beam axis 440, an angular deviation ofthe optical system is introduced. For example, if the folding mirror istilted at a 2° angle away from 45°, a sufficient offset is introducedinto the beam 439 to prevent the reflected beam 439 from being imagedback onto the fiber optic 430. When specular reflection of the focusedlaser beam 436 a occurs at the work piece surface 17, the beam 436 a isreflected away from the surface 17 at an angle equal to the angle ofincidence. The reflected beam 439 propagates back towards the foldingmirror 438 at an angle of 2° with respect to the normal to the workpiece surface 17. When the reflected beam strikes the folding mirror438, a second 2° offset is added to its direction of propagation withrespect to the optical axis 440 of the emergent beam 436. That is, thereflected beam 439 is now directed 40 away from the axis of the opticalfiber 430. In a preferred embodiment, the reflected beam 439 is imagedharmlessly on the water-cooled optical fiber holder 431 a distance awayfrom the optical fiber 430 itself. This small angular deviationintroduces a small displacement of the focused spot 17 from a pointnormal to the deposition surface 17. Through proper design, negativeeffects due to the different trajectory angle of the reflected beam 439through the powder stream intersection region 20 are negligible.

The focused beam 436 a is incident onto the surface 17 of the work 15 at20 from normal. The beam 436 a passes through the powder streamintersection region 20 at this angle also. If it is assumed that thedeposition occurs in a 0.100 inches long region of the powder streamintersection zone, that is along the work piece surface 17, the“pointing” error of the beam 436 a in the deposition plane is as about0.0035 inches. This error is negligible.

Zemax™, a commercially available optical design package, was used todetermine the offset as the beam 436, 439 was propagated through thecollimating and focusing lenses 433, 434. The prescription data anddetails used to model the lens are not included here. However, thepredicted location of the final specular-reflected beam image on thefiber holder 431 was displaced from the center of the optical fiber 430by approximately 0.310 inches. An image due to diffuse reflectionsshould be offset by at least half of this amount.

Although the offset image of the reflected beam 439 prevents thereflected laser energy from damaging the optical fiber 430, there isalso an issue of direct fiber heating by the laser beam 436 as it istransmitted through the optical fiber cable 430. To mitigate thiseffect, the output end of the fiber 430 is mounted in a water-cooledcopper block 431. The copper block 431 has an output aperture diameterof about 0.2 inches. The diameter was chosen to be sufficiently large toaccommodate the diverging output beam 436 from the fiber 430 withoutblocking the beam 436. At the edge of the aperture, the surface of thecopper block 431 is beveled at 45° to reflect any light incident ontothis surface outward away from the center line 440 of the fiber mount.The inner, rear surface of the block 431 traps the reflected light 439so that the laser energy can be absorbed in the fiber holder 431 wherethe heat can be subsequently carried away by cooling water.

The above system of laser beam 436 delivery has been performed whileoperating the laser at 900 watts and scanning the focused beam 436 a ona copper substrate 15 for approximately one hour. The copper substrate15 has a reflectivity of approximately 98% at the laser wavelength of1.064 μm. Essentially, all of the laser power was reflected back to thewater-cooled surface of the fiber holder 431. There was no degradationof the optical fiber 430 at its output.

11. Laser Beam Shutter

To cut-off the laser beam 125 while re-positioning the deposition head11 from place-to-place on the work piece 15, a laser beam shutterassembly 450 has been created for the DMD process such as outlinedbelow. FIGS. 34 and 35 are perspective views of the laser beam shutterassembly 450. FIG. 35 shows the assembly of FIG. 34 with the cover and asection of the liquid cooled beam “dump” 452 removed. The design of thebeam “dump” 452 for this shutter assembly 450 is unique. The beam dump452 is a liquid-cooled metal block 453 on which the laser beam 436 isfocused by the laser beam shutter mechanism 462. To allow operation athigh power, it is important to be able to spread the laser energy outover a large surface to avoid damage to any of the beam dump surfaces.Liquid is circulated through tubes 454 to cool the whole beam dump block453.

Probably the most important reason for avoiding damage to the beam dump450 is danger of generating vapor which will degrade optical surfacesnear a damaged dump surface. As with any optical surface, once somedamage has occurred, the surface quickly degrades to a point ofuselessness.

FIG. 35 a is a schematic sketch of the operation of the laser beamshutter mechanism 462 with the cooling caps 451 removed. The laser beam125 is interrupted by a mirror 465 which redirects the laser beam 125into the laser beam absorption chamber 466 through laser dump aperture468. The beam 125 falls on a first reflective, diverging surface 469.The divergent beam is reflected onto a second reflective surface 470 andthen onto surface 471 where it is absorbed. Creation of the divergentbeam may be by alternative means such as a lens, concave or convexreflective surface.

12. Multi-Axis Deposition Head

FIGS. 36 through 40 a reveal a multi-axis deposition head 480 which isdesigned to deposit materials in other directions in addition to thez-axis. The head 480 contains the powder delivery system integrally.When coupled with a three-axis stage which positions the deposition head480 in the x-y-z orthogonal axes, the deposition head 480 providesrotation 482 about a fourth axis u and rotation 484 about a fifth axisv. Of course, the work piece can also be moved in the x-y-z orthogonalaxes and the deposition head 480 held stationary.

FIG. 40 a shows how the deposition head 480 is continually positioned toproduce a three-dimensional, curved object 490. It is the relativemotion of the deposition head 480 and the work piece which creates thelines of material deposition, as has already been seen. Applying themulti-axis feature of the deposition head 480 enables three-dimensionalstructures of virtually every kind to be fabricated directly from a CADsolid model. In addition to the multi-axis head 480, robotic arms andtilting, rotating stages for the work piece are usable for fabricationof many three-dimensional structures. These features also facilitate useof transformations to various coordinate systems which accommodatespecific geometric configurations such as cylinders and spheres.

The multi-axis deposition head 480 includes the powder delivery system170 and optical fiber, laser beam delivery system 420 described above.FIG. 40 a illustrates how the multi-axis deposition head 480 ispositioned in order to produce a three dimensional, curved structure490. Controlled translation in three axes x, y and z and controlledrotation about two axes u an v are used to position the deposition head480 with respect to the work piece 490. Note that the translation of thehead in the x, y and z axes can be used in place of or in combinationwith the translation of stage 16.

13. Particle Beam Focusing to Reduce Material Waste

FIG. 41 depicts one of a plurality of powder delivery nozzles 14 of theprior art, which are disposed in a deposition head 11. In thisconfiguration, a stream of gas-entrained powder 502 exits a powder tube500 and tends to disperse away from the axis of the stream 502 becauseof expansion and deceleration of the gas.

FIG. 42 shows an improved powder delivery nozzle 504 used in the presentinvention. A coaxial flow tube 506 surrounds the powder tube 500 and iscoextensive with it. The bore of the coaxial flow tube is slightlylarger than the outside diameter of the powder tube 500. Gas 508 isforced to flow through the coaxial flow tube 506, between the outsidediameter of the powder tube 500 and the inner bore of the coaxial flowtube 506. The gas 508 forms a sheath-like column 510 surrounding theentrained powder 502 as it leaves the powder tube 500. The gas column510 provides a barrier to the entrained powder 502 and as a result, thepowder 502 is projected from the powder tube 500 in a coaxial stream,and remains so for an extended distance and time period.

The improved nozzle 504 projects a smaller, constant-diameter powderstream 502 for a longer distance than the prior art nozzle 14. As aresult, the powder delivery nozzle 504 can be located farther away fromthe deposition 15 surface with much less waste of material. Materialutilization efficiency depends on the ratio of area of the laser-createdmolten pool 17 to that of the powder stream 502 footprint on thedeposition 15 surface.

FIG. 43 reveals a still further improved powder delivery nozzle 515which increases the efficiency of directed material depositions with thepresent invention. A coaxial flow tube 520 which surrounds the powderdelivery tube 500 is constricted at the outlet 526 so the coaxial gascolumn 508 is directed inward toward the entrained powder stream 502 asthe powder stream 502 leaves the powder tube 500. Turbulence in thecoaxial gas column 528 concentrates the powder stream 502 and focuses itto a small footprint on the deposition surface. This innovation providesan even higher concentration of powder at the deposition 15 surface thanpowder delivery nozzle 504, the least waste and therefore the bestpowder utilization efficiency. The outlet orifice depicted in FIG. 43 isas approximately square edged, which is easily manufactured. A moreprecision, converging-diverging nozzle shape is an alternativeembodiment to the square-edged outlet 526.

The operation of the sheath-like column 510 which forms a “no-slip”fluid boundary layer may be better understood by referring to FIGS. 44and 45. FIG. 45 reveals a flow of powder entrained in gas 502 which ismoving at a velocity of V_(a). The coaxial gas flow has a velocity ofV_(b). The gas surrounding the powder tube 500 and coaxial flow tube 506in the environmentally controlled chamber 128 in which the depositiontakes place has a velocity of V_(c). Control of the velocities V_(a) andV_(b) is essential to the operation of the coaxial gas sheath 510. Flowrate conditions considering V_(a) and V_(b) and V_(c) are:

-   -   1. V_(a)≈V_(b); V_(c)≈0    -   2. V_(b)<<V_(a); V_(c)≈0    -   3. V_(b)>>V_(a); V_(c)≈0

FIG. 44 illustrates a flow rate condition where V_(a)≈V_(b) and V_(c)≈0.For this first condition, there is no significant change in thedirection of powder stream 502 as it leaves the powder tube 500. V_(b)will decrease at the edge of the coaxial gas stream 510 because thevelocity V_(c) of the gas in the environmentally controlled chamber 128is approximately zero. But the sheath formed by the coaxial gas flow 510maintains the focus of the entrained powder stream 502 until it strikesthe deposition surface 15.

However, if as in condition 2, V_(b) is much less than V_(a), then V_(b)“peels back” the entrained powder stream 502, de-focusing it and causingthe powder to spread out at the deposition surface 15.

In condition 3, depicted in FIG. 45, where V_(b) is much greater thanV_(a), an adverse situation develops in which the coaxial gas streammixes 532 with the entrained powder stream and the powder spreads outunacceptably at the deposition surface 15.

In respect of the improved nozzle 515 shown in FIG. 43, control of thegas velocities V_(a) and V_(b) is still important even though thelocalized turbulence caused by the orifice 526 helps to focus theentrained gas flow 502.

CONCLUSION

Although the present invention has been described in detail withreference to particular preferred and alternative embodiments, personspossessing ordinary skill in the art to which this invention pertainswill appreciate that various modifications and enhancements may be madewithout departing from the spirit and scope of the claims that follow.The various hardware and software configurations that have beendisclosed above are intended to educate the reader about preferred andalternative embodiments, and are not intended to constrain the limits ofthe invention or the scope of the claims. The List of ReferenceCharacters which follows is intended to provide the reader with aconvenient means of identifying elements of the invention in theSpecification and Drawings. This list is not intended to delineate ornarrow the scope of the claims.

List of Reference Characters

FIGS. 1 & 1 a

-   10 LENS™ apparatus, prior art-   11 Deposition head-   12 Laser beam-   13 Focusing lens-   14 Powder delivery nozzle-   15 Deposited material-   16 X-Y positioning stages-   17 Molten metal pool-   18 Z-axis positioning stage-   19 Substrate-   20 Laser beam-material powder interaction region-   Δt Deposition layer thickness    FIG. 2-   28 Sample object    FIG. 3-   30 Chart of Deposition Layer Thickness v. Laser Irradiance/Velocity-   32 Deposition Layer Thickness-   34 Laser Irradiance/Velocity    FIG. 4-   40 Graph of Average Surface Roughness vs. Material Particle Size-   42 Average Roughness-   44 Particle Size-   46 Legend: Average Roughness and Laser Power    FIG. 4 a-   47 0.2% yield strength-   49 Laser-exposure factor-   48 Tensile Strength vs. Exposure graph    FIG. 5-   50 Unheated substrate-   51 Upper surface of unheated substrate-   52 Pre-heated substrate (100° C.)-   53 Upper surface of preheated substrate (100° C.)-   54 Preheated substrate (200° C.)-   55 Upper surface of preheated substrate (200° C.)-   56 Deformation of first substrate-   56 a Deformation of second substrate    FIGS. 6 & 7-   70 Directed material Deposition (DMD) apparatus with heated    substrate-   12 Laser beam-   13 Beam focusing lens-   14 Powder delivery nozzle-   15 Material deposition-   16 x-y axis position stages-   18 z-axis positioning stage-   17 Molten metal pool-   19 Substrate-   72 Radiant heating source-   74 Radiant heat-   76 Temperature sensor/pyrometer-   80 Directed material deposition apparatus with heated platen-   81 Heated platen and x-y positioning stages-   82 Heating element-   84 Platen temperature sensor-   86 Substrate temperature sensor    FIG. 8-   90 Temperature profile chart for DMD processing-   92 Temperature-   94 Time-   95 Temperature cycle: controlled temperature increase-   96 Temperature cycle: steady temperature maintained-   97 Temperature cycle: controlled temperature decrease    FIG. 9-   100 Comparison deformation of deposition for heated and unheated    substrates-   15 Deposition on heated substrate-   15 a Deposition on unheated substrate-   19 Heated substrate-   19 a Unheated substrate    FIG. 10-   110 Temperature profile chart for DMD processing-   92 Temperature-   94 Time-   112 Temperature ramp-up-   114 Steady state temperature-   116 Temperature decrease to above room temperature-   117 Steady state, elevated temperature-   118 Second cycle: Temperature ramp-up-   120 Steady state, high temperature-   122 Temperature ramp-down to room temperature    FIG. 11-   123 Directed Material Deposition apparatus-   11 Deposition head with focusing lens-   15 Deposited material-   16 x-y axis positioning stages-   18 z-axis positioning stage-   19 Substrate-   20 Laser beam-material powder interaction region-   124 Laser-   125 Emitted laser beam-   125 a Focused laser beam-   126 First material storage-   127 Second material storage-   128 Environmentally controlled chamber-   129 Computer, controller-   129 a Computer monitor-   129 b Computer signals to positioning stages    FIGS. 12 Through 14-   130 Solid model of a first material captured within a solid model of    a second material-   132 Inner block made of a first material-   134 Outer block made of second material-   136 Region of overlapping solid models and composite material-   138 Hatch-fill lines of deposition of second material-   140 Boundary of composite material-   141 Cross-section of solid model of second material-   142 Hatch-fill lines of deposition of first material-   144 Outer boundary of block of first material; inner boundary of    composite material region-   146 Cross-section of solid model of first material    FIGS. 14 a & 14 b-   149 Rapid-acting metering valve-   150 Gas and powder inlet port-   150 a Gas and powder waste-   150 b Gas and powder to delivery path (to work piece)-   151 Gas only inlet port-   151 a Gas to reclamation-   151 b Gas to powder delivery path-   152 Valve body-   153 Outlet port, powder delivery to work piece-   154 Waste powder outlet port-   155 Gas flow to powder delivery path, outlet port-   156 Diverter plunger-   158 Diverter passages-   159 Powder flow rate sensor-   Gp Gas and powder input flow-   G Gas input flow    FIGS. 15, 16, 16 a-   170 Powder feed unit-   172 Powder reservoir-   174 Gas and powder flow to deposition head-   175 View ports-   176 Reservoir lid-   178 Transfer chamber-   179 Powder feed disk-   180 Motor-   181 Powder receptacles-   182 Motor controller-   183 Rotational axis-   184 Wiper assembly-   185 Powder mound-   186 Gas inlet-   187 Powder and gas stream to work piece-   188 Gas and powder outlet-   189 Mounting bracket-   190 Powder feed tube    FIG. 16 b-   200 Flow rate axis-   202 RPM axis    FIG. 16 c-   210 First dissimilar material-   212 First transitional material deposition-   214 Second transitional material deposition-   216 Second dissimilar material    FIGS. 17 & 18-   250 Cut-away view of injection mold insert with integral cooling    passages-   252 Cooling passages-   254 Mold cavity-   256 Mold block-   258 Cross-sectioned face of mold block-   259 Finned structure separating cooling passages-   260 Cooling medium inlet-   262 Cooling medium outlet    FIG. 19-   270 Cross-section of solid rectangular article with uniform-flow    cooling passages-   272 Cooling medium inlet-   274 Cooling medium outlet-   276 Cooling passage-   278 Cooling medium inlet reservoir-   279 Cooling medium outlet reservoir    FIG. 20-   280 Cross-section of a cylindrical article of random length with    integral cooling passages-   282 Cooling passages    FIG. 21-   286 Cross-section of a cylindrical shape with multiple independent    loops of cooling passages and a plurality of cooling channels 189    having a common reservoir-   288 Independent cooling passages-   289 Cooling channels with a common reservoir    FIG. 22-   290 Solid, curved object having integral cooling passages which    follow the contour of the outer shape of the object-   292 Cooling passages    FIG. 23-   300 Airfoil-shaped article having length, curvature and twist, with    integral cooling passages-   302 Cooling passages    FIGS. 24 Through 26 c-   310 Completed substrate-   310 a Partially completed substrate-   310 b Partially completed substrate with partially completed upper    surface-   312 External surfaces-   314 Internal cavities-   316 Partially completed upper surface-   318 Latticed substrate-   319 Tubular cooling channels structure-   320 Latticed substrate support surface-   322 Injection mold substrate with embedded cooling channels-   323 Upper surface of mold-   324 Cooling channels-   325 Molding surface    FIGS. 27 Through 32-   14 Deposition head-   15 Material deposition-   20 Laser beam-powder interaction zone-   340 Focused laser beam-   342 Powder stream-   344 Material bead deposition at the part edges-   346 Overhanging structure-   348 Deposition layer-   θ Work piece rotation-   Δx Material bead overhang dimension    FIG. 33-   15 work piece deposition-   17 molten pool, deposition plane-   420 laser delivery system-   430 optical fiber-   431 water-cooled fiber holder-   433 collimating lens-   432 laser beam center line-   434 focusing lens-   436 deposition laser beam-   436 a focused deposition laser beam-   438 folding mirror-   439 reflected laser beam-   440 reflected laser beam image-   441 lens housing    FIGS. 34, 35 & 35 a-   450 laser beam shutter “dump” assembly-   451 cooling caps-   452 laser beam “dump”-   453 “dump” block-   454 cooling fluid tubes-   455 shutter aperture-   460 cut-away view of laser beam shutter “dump” assembly-   461 light path diagram-   462 shutter mechanism-   464 shutter actuator-   465 mirror-   466 laser beam absorption chamber-   468 aperture, beam “dump”-   469 diverging first surface-   470 reflective second surface-   471 absorbent surfaces    FIGS. 36 Through 40 a-   16 stage-   125 a focused laser beam-   480 multi-axis deposition head-   482 rotation about u-axis-   484 rotation about v-axis-   x, y, z orthogonal translation axes    FIGS. 41 Through 45-   14 powder delivery nozzle of prior art-   15 deposition-   500 powder tube-   502 entrained powder stream-   504 improved powder delivery nozzle with axial-flow gas tube-   506 coaxial gas flow tube-   508 coaxial gas flow-   510 coaxial gas column and turbulence-   515 improved powder delivery nozzle with axial-flow gas tube    restrictor.-   520 coaxial flow gas tube with restrictor-   526 gas tube restricted outlet-   528 restricted gas column and turbulence-   530 deposition footprint of powder stream-   532 coaxial gas flow and entrained powder stream mixing-   V_(a) velocity of entrained powder stream-   V_(b) velocity of coaxial gas stream-   V_(c) velocity of gas in environmentally controlled chamber (128)

1. A powder feeder comprising: a chamber; an inlet for providing powderto said chamber, the powder forming a pile in said chamber; a rotatingdisk partially immersed in said pile, said disk comprising a pluralityof circumferentially disposed receptacles for picking up and removingpowder from said pile; and a wiper assembly for removing the powder fromsaid receptacles.
 2. The powder feeder of claim 1 wherein an angle ofrepose of said pile continuously limits a flow of powder into saidchamber.
 3. The powder feeder of claim 2 wherein said disk is notclogged by the powder.
 4. The powder feeder of claim 1 wherein saidreceptacles comprise holes in said disk.
 5. The powder feeder of claim 1wherein said receptacles bring a controlled volume of powder to saidwiper assembly.
 6. The powder feeder of claim 1 wherein a spacing ofsaid wiper assembly from said disk is chosen to minimize contact betweenthe powder and said wiper assembly.
 7. The powder feeder of claim 6wherein wear of said wiper assembly is substantially reduced.
 8. Thepowder feeder of claim 1 wherein said wiper assembly provides a firstgas flow substantially perpendicular to said disk.
 9. The powder feederof claim 8 wherein said first gas flow comprises a flow of an inert gas.10. The powder feeder of claim 8 wherein said powder feeder isinsensitive to variations in a rate of said first gas flow.
 11. Thepowder feeder of claim 8 wherein said first gas flow clears powder fromsaid receptacles and entrains the powder, thereby providing a powderflow.
 12. The powder feeder of claim 11 wherein said first gas flowfluidizes the powder.
 13. The powder feeder of claim 11 wherein a rateof said powder flow is proportional to a rotational speed of said disk.14. The powder feeder of claim 11 wherein a rate of said powder flow isas low as approximately 0.1 grams per minute.
 15. The powder feeder ofclaim 11 wherein a rate of said powder flow is linear betweenapproximately 0.1 grams per minute and approximately 30 grams perminute.
 16. The powder feeder of claim 11 further comprising: a gasinlet providing a second gas flow; a spool valve assembly comprising aplunger, said plunger comprising a plurality of passages for divertingfrom one to one hundred percent of said powder flow to a first wastestream and diverting from one to one hundred percent of said second gasflow to a second waste stream; an outlet for mixing an undivertedportion of said powder flow together with an undiverted portion of saidsecond gas flow to form a final powder mass flow having a controlledrate; and at least one outlet for collecting waste gas and powder. 17.The powder feeder of claim 16 further comprising a flow rate controllerfor each of said powder flow and said second gas flow.
 18. The powderfeeder of claim 16 through which gas is constantly flowing.
 19. Thepowder feeder of claim 16 comprising a sufficient gas flow to preventpowder from settling out of said powder flow or said final powder massflow.
 20. The powder feeder of claim 16 wherein said plunger is rapidlymoveable within said spool valve assembly.
 21. The powder feeder ofclaim 20 wherein said controlled rate of said final powder mass flow israpidly variable.
 22. The powder feeder of claim 21 wherein saidcontrolled rate of said final powder mass flow is variable from nopowder to a mass flow rate of said powder flow.
 23. The powder feeder ofclaim 16 wherein a position of said plunger is controllable by acomputer.
 24. The powder feeder of claim 16 further comprising a massflow sensor.
 25. The powder feeder of claim 24 further comprising afeedback loop for control of said final powder mass flow rate.
 26. Amaterial deposition apparatus comprising at least one of said powderfeeders according to claim
 16. 27. The material deposition apparatus ofclaim 26 for depositing a first powder and a second powder, saidapparatus rapidly controlling relative proportions of the first powdersupplied from a first powder feeder and the second powder supplied froma second powder feeder.
 28. The material deposition apparatus of claim27 wherein said apparatus deposits three-dimensional gradient materialstructures.
 29. The material deposition apparatus of claim 27 whereinsaid apparatus deposits a buttering layer.
 30. A method for providing apowder flow, the method comprising the steps of: forming a pile ofpowder; continuously limiting a size of the pile; moving a quantity ofthe powder from the pile to a first gas flow; and entraining the movedpowder in the first gas flow to form a powder flow.
 31. The method ofclaim 30 wherein the limiting step comprises blocking a powder supplytube until the pile collapses, thereby temporarily unblocking the tube.32. The method of claim 30 wherein the moving step comprises fillingwith powder a plurality of receptacles circumferentially disposed in arotating disk.
 33. The method of claim 32 wherein the receptaclescomprise holes in the disk.
 34. The method of claim 32 furthercomprising the step of partially immersing the disk in the pile.
 35. Themethod of claim 34 further comprising preventing clogging of the disk.36. The method of claim 30 further comprising the step of controllingthe quantity of the powder being moved.
 37. The method of claim 30wherein the entraining step comprises fluidizing the powder.
 38. Themethod of claim 32 wherein a powder flow rate is proportional to arotational speed of the disk.
 39. The method of claim 30 wherein apowder flow rate is as low as approximately 0.1 grams per minute. 40.The method of claim 30 wherein a powder flow rate is linear betweenapproximately 0.1 grams per minute and approximately 30 grams perminute.
 41. The method of claim 30 further comprising the steps of:providing a second gas flow; diverting from zero to one hundred percentof the powder flow to a first waste stream; diverting from zero to onehundred percent of the second gas flow to a second waste stream; andmixing an undiverted portion of the powder flow together with anundiverted portion of the second gas flow to form a final powder massflow.
 42. The method of claim 41 further comprising the step ofcollecting waste gas and powder from the first waste stream and thesecond waste stream.
 43. The method of claim 41 further comprising thestep of separately controlling a rate of the second gas flow and a rateof the powder flow.
 44. The method of claim 41 further comprisingproviding sufficient gas flow to prevent powder from settling out of thepowder flow or the final powder mass flow.
 45. The method of claim 41further comprising the step of controlling a rate of the final powdermass flow.
 46. The method of claim 45 wherein the controlling stepcomprises rapidly varying the rate of the final powder mass flow. 47.The method of claim 45 wherein the controlling step comprises using acomputer.
 48. The method of claim 45 wherein the controlling stepcomprises varying the rate of the final powder mass flow from no powderto a mass flow rate of the powder flow.
 49. The method of claim 45further comprising the step of measuring the rate of the final powdermass flow.
 50. The method of claim 49 further comprising the step ofproviding a feedback loop for controlling the rate of the final powdermass flow.
 51. The method of claim 41 further comprising the step ofdepositing powder from the final powder mass flow.
 52. The method ofclaim 51 further comprising the step of depositing a first powder fromthe final powder mass flow and a second powder from a second finalpowder mass flow.
 53. The method of claim 52 further comprising the stepof rapidly controlling relative proportions of the first powder and thesecond powder during deposition.
 54. The method of claim 53 wherein thedepositing step comprises depositing three-dimensional gradient materialstructures.
 55. The method of claim 53 wherein the depositing stepcomprises depositing a buttering layer.